Recently, terminals provide not only a basic communication function but also various functions including a multimedia photographing and reproducing function, a game function, a digital broadcasting function, a wireless Internet function, etc. Such a terminal generally uses a battery for the purpose of portability.
The battery of the terminal requires charging. The charging method of the battery may be a wired charging method and a wireless charging method. The wired charging method is currently generalized, but a wireless charging system using an electromagnetic induction phenomenon has recently been developed. The wireless charging system uses a method of applying power to a wireless power transmitter having a coil included therein and charging a battery using induction current generated in a coil included in a terminal or battery due to the electromagnetic field generated in the coil of the wireless power transmitter, and the method is divided into inductive coupling and electromagnetic resonance coupling. That is, in the wireless charging system, the terminal is positioned within the range of the wireless power transmitter generating an electromagnetic field, so that the charging of the battery can be easily performed.
However, when the distance from the wireless power transmitter to the terminal is increased or when the position of the terminal is separated from a certain range of the wireless power transmitter, the charging efficiency of the wireless charging method using the inductive coupling is lowered. Therefore, when the terminal is separated from the range of the wireless power transmitter, the terminal cannot be charged to the maximum efficiency so as to perform various functions of the terminal. Accordingly, it is necessary to easily perform the functions of the terminal without separating the terminal from the range of the wireless power transmitter.
To satisfy such a necessity, a charging method using the electromagnetic resonance coupling has been developed, which prevents the lowering of the charging efficiency according to the distance between the wireless power transmitter and the terminal, but there is still an inconvenience in using the terminal during the charging of the terminal.